Method to transmit downlink signaling message on cellular systems for packet transmission and method for receiving the message

ABSTRACT

Provided is a downlink control information transmitting and receiving method which can maximize the use of limited radio resources by effectively forming an uplink signaling message to be transmitted from a base station to a terminal and transmitting the formed uplink signaling message with a minimum amount of radio resources occupied. The method for transmitting downlink data generation indication information for a base station to inform a terminal of packet data transmission in a packet-based cellular system, includes the steps of: a) generating the downlink data generation indication information; b) recording radio resource allocation information in downlink scheduling information for transmitting the downlink data generation indication information, and allocating information for the downlink data generation indication information to downlink-shared radio resources; and c) transmitting the downlink scheduling information and the information for the downlink data generation indication information according to a transmission cycle.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.12/305,891, filed Dec. 19, 2008, pending, which is based upon and claimsthe benefit of priority of the prior PCT International ApplicationNumber PCT/KR2007/003016, filed Jun. 21, 2007 and Korean ApplicationNos. 10-2006-0056004, filed Jun. 21, 2006, and 10-2006-0077262, filedAug. 16, 2006, the entire contents of all of which are incorporated byreference herein.

TECHNICAL FIELD

The present invention relates to a method for transmitting and receivingdownlink signaling message in a packet-based cellular system; and, moreparticularly, to a downlink control information transmitting andreceiving method which can maximize the use of limited radio resourcesby effectively forming an uplink signaling message to be transmittedfrom a base station to a terminal and transmitting the formed uplinksignaling message with a minimum amount of radio resources occupied.

BACKGROUND ART

A conventional Wideband Code Division Multiple Access (WCDMA) is acircuit based system that transmits control information such as asignaling message from a base station to a terminal using a downlinkdedicated channel. A long term evolution (LTE) system was introduced asa packet-based system and has been standardized for providing variouspacket services, and there have been many researches in progress forfinding a method for effectively and variably using radio resources forthe LTE system.

The long term evolution (LTE) system is a technology that realizes ahigh-speed packet-based communication, for example, about 100 Mbps. Itis expected that the LTE system will be commercialized by around 2010.An Orthogonal Frequency Division Multiplexing Access (OFDMA) has beenconsidered to be used for the LTE system. Unlike a Code DivisionMultiple Access (CDMA) that distinguishes radio resources of eachterminal by allocating codes, the OFDMA system has two dimensional radioresources distinguished by a frequency and a time. That is, the OFDMAsystem transmits and receives radio resources constituted of time andfrequency for uplink physical channel and downlink physical channel.Also, the OFDMA system uses radio resource blocks divided by atransmission time interval (TTI) as a transmission period and asubcarrier group. A radio frame constituting such radio resources isformed of 0.5 millisecond slots or TTIs. Therefore, one radio frame isformed of 20 slots in case of a 10-millisecond radio frame.

Unlike a circuit system that dedicatedly allocates radio resources toterminals, the packet-based LTE system allows terminals to share radioresources to transmit a packet service data. The LTE system allocatesradio resources according to a radio channel condition of a terminal,which dynamically changes according to whether the necessity of datatransmission and according to a time. Therefore, the LTE system needs amethod for providing uplink control information to various terminalsthrough a radio resource in order to enable each of terminals todiscriminate radio resources allocated to itself from radio resourcesallocated to the others, access, and modulate the allocated radioresource according to a cycle of allocating a radio resource. Also, theLTE system needs a method for forming an uplink control information tovariably and flexibly use physical layer radio resource and a method fortransmitting the uplink control information.

In order to satisfy such a demand, there was a discussion in progress toclassify radio resources into a local allocated radio resource and adistributed allocated radio resource for adaptively allocating and usingradio resources corresponding to a wireless environment. In order toeffectively allocate these two radio resources, it has been consideredto transmit the control information such as a signaling message using acontrol channel that is shared with a plurality of terminals instead ofusing a dedicated control channel like the conventional WCDMA and totransmit some of control information using radio resources allocated toeach of terminals.

That is, there is a demand for developing a method for effectivelyforming uplink control information such as an uplink signaling messageusing a downlink from a base station to a terminal and transmitting theuplink control information with minimum radio resource occupied, therebyimproving the usability of limited radio resources.

DISCLOSURE Technical Problem

An embodiment of the present invention is directed to providing a methodfor transmitting and receiving downlink control information in apacket-based cellular system, which can maximize the use of limitedradio resource by effectively forming a uplink signaling message totransmit from a base station to a terminal and transmitting the formeduplink signaling message with minimum radio resource occupied.

Other objects and advantages of the present invention can be understoodby the following description, and become apparent with reference to theembodiments of the present invention. Also, it is obvious to thoseskilled in the art of the present invention that the objects andadvantages of the present invention can be realized by the means asclaimed and combinations thereof.

Technical Solution

In accordance with an aspect of the present invention, there is provideda method for transmitting downlink data generation indicationinformation for a base station to inform a terminal of packet datatransmission in a packet-based cellular system, the method including thesteps of: a) generating the downlink data generation indicationinformation; b) recording radio resource allocation information indownlink scheduling information for transmitting the downlink datageneration indication information, and allocating information for thedownlink data generation indication information to downlink-shared radioresources; and c) transmitting the downlink scheduling information andthe information for the downlink data generation indication informationaccording to a transmission cycle.

In accordance with another aspect of the present invention, there isprovided a method for receiving control information transmitted from abase station of a packet-based cellular system, the method including thesteps of: a) confirming radio resource allocation information indownlink scheduling information; b) confirming a radio resource blocklocation allocated from the radio resource allocation information whenthe radio resource allocation information includes an own identifier;and c) obtaining the control information transmitted with correspondingradio resources using the confirmed radio resource block locationinformation.

Advantageous Effects

A method for transmitting and receiving downlink control information ina packet-based cellular system according to an embodiment presentinvention can maximize the utility efficiency of limited radio resourcesby effectively forming an uplink signaling message to be transmittedfrom a base station to a terminal and transmitting the formed uplinksignaling message with a minimum amount of radio resources occupied.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates transmission of grant information for responding torandom access in accordance with an embodiment of the present invention.

FIG. 2 illustrates transmitting downlink packet generation indicationinformation in accordance with an embodiment of the present invention.

FIG. 3 is a diagram illustrating a group identifier of downlinkscheduling information in accordance with an embodiment of the presentinvention.

FIG. 4 is a diagram illustrating exclusively allocating and using adistributed allocated radio resource for transmitting downlink controlinformation in accordance with an embodiment of the present invention.

BEST MODE FOR THE INVENTION

The advantages, features and aspects of the invention will becomeapparent from the following description of the embodiments withreference to the accompanying drawings, which is set forth hereinafter.

At first, a base station generates control information such as asignaling message to be transmitted to terminals. The controlinformation, transmitted from a base station to terminals, includesscheduling control information allocated to each of terminals by a basestation for one TTI or for predetermined TTIs, response information foruplink random access, and downlink data generation indicationinformation for terminals that operate in a low power consumption mode.

The control information such as the signaling message, transmitted froma base station to each of terminals for uplink scheduling, may includeradio resource allocation information, modulation and codinginformation, and retransmission information.

The radio resource allocation information may include information abouta scheduling identifier, a radio resource block location, and a radioresource allocation duration. The scheduling identifier is informationabout a terminal or a terminal group where the allocated radio resourcesbelong. The radio resource block location is information to addressradio resources of an Orthogonal Frequency Division Multiple Access(OFDMA) where radio resources are divided in a frequency domain and atime domain. The radio resource allocation duration is information abouta valid duration of the allocated radio resources.

The modulation and coding information may include transport formatinformation and a multi input multi output (MIMO) related information.The transport format information includes a modulation scheme applied toallocated radio resources, such as QPSK, 16QAM, or 64QAM, and a payloadside or a coding level. That is, the transport format information isinformation to calculate an encoding level by providing the payload sizeto be transported through the allocated radio resources or to directlyprovide the encoding level. The MIMO related information is controlinformation necessary to improve the performance of a system bytransmitting and receiving using the multiple antennas.

The retransmission information is information related to retransmitpacket data which is transmitted using allocated radio resources.

The response information for random access, which is transmitted from abase station to terminals that tried random access, may include radioresource allocation information, scheduling identifier information,positive acknowledgement (ACK) and negative acknowledgement (NACK) bitmap information, timing adjustment (TA) information, and power levelinformation. The response information may further include frequencyadjustment (FA) information.

The radio resource allocation information includes information about aterminal identifier and a radio resource block location. The terminalidentifier is information about a terminal or a terminal group thatincludes uplink radio resource allocated for random access response. Asignature index used for random access or an RA-preamble identifier canbe used as the terminal identifier. The radio resource block location isinformation for addressing uplink radio resource available to terminalsthat try random access.

The scheduling identifier is an identifier allocated to a terminal by abase station or a scheduler for the base station or the scheduler toidentifier terminals. For example, a schedule ID or a MAC ID can be usedas the scheduler identifier. The scheduler uses a scheduling identifierwhen control information such as scheduling information to allocateradio resources is transmitted. Therefore, a scheduler allocates ascheduling identifier when response information is transmitted to aterminal trying random access.

The ACK/NACK bit map information is information about whether a basestation receives the preamble signatures of terminals. The ACK/NACK bitmap information is formed as a bit map according to the index of thepreamble signature that forms an uplink random access burst. TheACK/NACK bit map information includes corresponding bit map informationset as ‘1’ when a base station detects a preamble signature transmittedby a terminal or includes corresponding bit map information set as ‘0’when a base station cannot detect the preamble signature transmitted bya terminal.

The timing adjustment information is timing information to reduce atiming error estimated by a base station using a random signal sequencepattern, i.e. the pattern of preamble or signature for initial randomaccess, for a terminal to sustain uplink synchronization and to adjustfor securing uplink physical layer synchronization, where the signalsequence pattern may be a signature or a predetermined symbol pattern,which are transmitted when initial random access is tried.

The power level information is information about a power reference levelto set a power level used when a terminal transmits to an uplink using apower level estimated by a base station using a random signal sequencepattern, for example, a signature or a predetermined symbol patternwhich is transmitted for initial random access, for a terminal tosustain the uplink synchronization.

The frequency adjustment information is frequency information to reducea frequency error estimated by a base station using a random signalsequence pattern, for example, a signature and a predetermined symbolpattern transmitted when initial random access, for a terminal tosustain uplink synchronization and to adjust for a terminal to secureuplink physical layer synchronization.

It is essential for a terminal to have a low power consumption functionin a packet-based cellular system. For this, terminals perform a lowpower consuming operation using discontinuous reception cycle(DRX)/discontinuous transmission cycle (DTX) set by a base stationaccording to the burst characteristics of packet data, such as theactivity of a terminal (UE activity), after a radio bearer is set with abase station. When a base station generates information to transmit tocorresponding terminals, downlink data generation indication informationis required to inform the corresponding terminals of the generation ofthe information.

The downlink data generation indication information includes radioresource allocation information and modulation and coding information.The radio resource allocation information includes a schedulingidentifier and radio resource location information. The schedulingidentifier is information for a scheduler in a base station to identifya terminal by allocating the scheduling identifier to the terminal or aterminal group for low power consuming operation when a low powerconsuming operation begins.

The modulation and coding information includes transport formatinformation. The transport format information includes a modulationscheme applied to allocated radio resources, such as QPSK, 16QAM, or64QAM, and a payload side or a coding level. That is, the transportformat information is information to calculate a coding level byproviding the payload size to be transported through the allocated radioresources or to directly provide the encoding level.

A base station transmits such control information including schedulingcontrol information, response information for random access, or downlinkdata generation indication information to a terminal by allocating thecontrol information to a downlink-shared radio resource for packet datatransmission.

In an OFDMA scheme which is considered to be used in a packet-basedmobile communication system such as a LTE system, terminals share twodimensional radio resources which are distinguished by frequency andtime. That is, downlink and uplink physical channels transmit radioresources formed of time and frequency, and a radio resource uses aradio resource block divided by a transmission cycle TTI and asubcarrier group which is a subcarrier index.

As a method for allocating control information to downlink-shared radioresource block, a radio resource is variable allocated using downlinkscheduling information, and a part of radio resources is exclusivelyallocated and used.

A method for variably allocating control information to a radio resourceusing downlink scheduling information, and a method for exclusivelyallocating control information to a radio resource will be describedwith reference to accompanying drawings.

A terminal confirms the relations between radio resources and terminalscheduling identifiers by searching uplink scheduling informationtransmitted on downlink at every transmission time interval (TTI). Then,the terminal checks a corresponding radio resource location and a radioresource allocation region when its own scheduling identifier or ascheduling identifier of an own group is included in the uplinkscheduling information. After checking, the terminal encodes andmodulates packet data with a radio resource allocated to oneself usingmodulation and coding information. Meanwhile, the terminal checks therelation between radio resources and terminal scheduling identifiers bysearching downlink scheduling information transmitted to a downlink atevery TTI. Then, the terminal confirms a corresponding radio resourcelocation and a radio resource allocation region when a schedulingidentifier or a scheduling identifier of its group is included in thedownlink scheduling information. After confirming, the terminal decodesand demodulates packet data with a radio resource allocated oneselfusing demodulation and decode information. Also, the terminal performs ahybrid automatic repeat request (HARQ) operation using theretransmission information of uplink control information.

The control information is encoded before it is transmitted on downlinkin order to sustain the quality thereof at a predetermined constantlevel on wireless channel. The control information for terminals may bejointly coded or separately coded. In order to secure the efficiency ofa system, the control information must be transmitted by occupying aminimum amount of radio resources. Also, the predetermined level of thequality must be secured in a wireless region with the minimum amount ofradio resources, and the performance of the system should be improved.

The scheduling information for downlink and uplink radio resources,which is transmitted at every TTI, must always occupy a predeterminedpart of a resource forming a TTI, and the amount of radio resourcesallocated for control information must be satisfied by signalingoverhead that is required by a system. That is, although a predeterminedpart of radio resources forming a TTI is allocated as a radio resourceto transmit control information such as scheduling, the amount of radioresources allocated for packet data should be satisfied by the signalingoverhead required by a system. For example, radio resources fortransmitting control information in a TTI occupy about 10% to 20% of theentire radio resources in a TTI.

Therefore, all of the control information cannot be transmitted usingradio resources for transmitting control information. Accordingly, ascheduler may use radio resources for control information to transmitscheduling information which is radio allocation information fordownlink and uplink that must be transmitted at every TTI. The schedulermay use radio resources allocated for packet data to transmit controlinformation required for event generation (event-driven signaling).

Downlink response(grant) information and downlink data generationindication information can be transmitted by variably allocating radioresources for packet data transmission using downlink schedulinginformation. Otherwise, they are transmitted by exclusively allocating apredetermined part of radio resources. The downlink response informationmay be downlink grant information for response to an uplink for randomaccess, and the downlink data generation indication information is forinforming terminals of the generation of information to transmit from abase station to corresponding terminals in low consumption operationmode.

When such information is transmitted by exclusively allocating apredetermined part of radio resources, the exclusively allocateddownlink radio resources for transmitting the grant information areradio resources that are searched only by terminals that try randomaccess. Therefore, the radio resources can be used to transmit packetdata for the other terminals or to transmit another control informationwhen there is not terminal trying random access. Also, the exclusivelyallocated downlink radio resource for transmitting the downlink datageneration indication information is a radio resource that should besearched by a terminal in a low power consumption mode for confirmingwhether downlink data is generated or not while a downlink is monitoredaccording to a DRX/DTX cycle.

That is, the method for using downlink scheduling information fortransmitting response information for random access can be summarized asfollows. A part of a scheduling identifier used for scheduling isreserved and allocated as a group scheduling identifier, and thetransmission of response information for random access is addressedusing the group scheduling identifier. Therefore, the terminals cancheck a group scheduling identifier and allocated radio resources forinforming the transmission of the grant information for random access bysearching downlink scheduling information. After the terminals confirmthe group scheduling identifier, each of the terminals obtains datatransmitted with a shared radio resource of an allocated radio resourcelocation based on the corresponding group scheduling information,demodulates and decodes the obtained data. As a result, each of theterminals can obtain response information for random access, which istransmitted from a base station.

FIG. 1 is a diagram illustrating a procedure of transmitting grantinformation with radio resources allocated by downlink schedulinginformation using a group scheduling identifier as an response forrandom access in accordance with an embodiment of the present invention.

If the grant information is transmitted as the response for randomaccess using radio resources allocated by downlink schedulinginformation, proper radio resources cal be allocated according towhether the existence of the response for random access or the sizethereof. If it is necessary, the control information may be transmittedusing the most robust and adaptive modulation and coding method.

In order to transmit response information for random access as shown inFIG. 1, radio resource allocation information 13 is set into apredetermined part of downlink scheduling information 12. The radioresource allocation information includes information about a schedulingidentifier, an allocated radio resource block location, and a radioresource allocation duration. The scheduling identifier is set to agroup scheduling identifier which is reserved and allocated for anresponse for random access. The allocated radio resource block locationinformation denotes the location of grant information allocated to ashare radio resource. The grant information is variably local-allocated14-1 or distributed-allocated 14-2 according to the amount ofinformation to be transmitted to a terminal. Herein, thelocal-allocation 14-1 is a transmission scheme that allocates controlinformation to a predetermined subcarrier index to transmit the controlinformation to a predetermined terminal.

The distributed allocation 14-2 is a transmission scheme thatdistributes control information to subcarrier indexes at a regularinterval to transmit the control information to a predeterminedterminal.

Meanwhile, the grant information included in the local-allocated or thedistributed-allocated radio resources has information elements (IE)shown in FIG. 1.

Terminals confirm a group scheduling identifier for transmitting controlinformation and shared radio resource block information allocatedthereto by searching downlink scheduling information and obtain controlinformation including the grant information or downlink data generationindication information by demodulating and decoding data transmitted bythe allocated radio resources.

Terminals check ACK/NACK bit map information 2 and grant IE numberinformation 3 among the obtained grant information, at first. Each ofthe terminals confirms whether a base station receives an own preamblesignature or not by searching the ACK/NACK bit map information which isformed in a bit map according to the index of a preamble signatureforming uplink random access burst, located at the foremost of theinformation. If bit information corresponding to the own preamblesignature is set as ‘1’, it means that the base station receives the ownsignature. On the contrary, if bit information corresponding to the ownpreamble signature is set as ‘0’, it means that the base station did notreceive the preamble signature tried by oneself.

If the bit map information is set to ‘0’, the terminal retries randomaccess without back-off. However, the terminal checks the number ofinformation elements in a grant message by searching the grant IE numberinformation 3 if the bit map information is set to ‘1’. Since theterminal directly retries random access without back-off if the bit mapinformation is set to ‘0’ as described above, unnecessary control planedelay can be reduced.

Although it was described that a base station puts ACK and NACK in bitmap information as a response for random access and transmits it in thepresent embodiment, a base station may transmit the acknowledgement to aterminal only for NACK in another embodiments.

After the terminal checks the grant IE number information, the terminalsearches grant information IE 4. An index of a signature used for randomaccess or an additional identifier such as random identity can be usedas a random access try identifier 5 of the grant information IE 4. Theterminal checks a scheduling identifier 6 in the IE when the randomaccess try identifier in the grant information IE is identical to arandom access try identifier of the own preamble signature transmittedby itself. Then, the terminal transmits own information such as radioresource control (RRC) connection information to an uplink using uplinkradio resource block location 7 information allocated to itself. Herein,uplink timing synchronization is controlled using TA information 8 inthe grant information IE. If it is necessary, the grant information IEincludes FA information 9 and power level information 10 to properuplink transmission. The terminal can properly set a power level or afrequency using the FA information 9 and the power level information 10for uplink transmission.

An extension bit (EB) 11 denotes whether another IE is present or notafter the grant information IE 4. If another IE is present, the EB 11 isset to ‘0’, and if the grant information IE 4 is the last informationelement, the EB 11 is set to ‘1’.

Meanwhile, the EB 11 can be used to denote whether any other informationIE is present after each information IE in a grant information block oran uplink scheduling information block if the grant message is formedwithout the grant IE number information 3 used.

If a terminal cannot detect grant information IE including a randomaccess try identifier that represents an own preamble signature althoughthe ACK/NACK bit map information is set to ‘1’, the terminal determinesthat grant information is not included by a base station due tofollowing cases although a base station successfully detects a preamblesignature. That is, if transmitted random access supplementaryinformation such as a reason of random access or priority information isnot normal, if a received preamble signal is excessively high, or ifavailable radio resources are not proper, a base station do not putgrant information for corresponding terminals in the grant information.Therefore, a corresponding terminal tries random access using parametersset for a random access procedure after a predetermined time passesaccording to back-off. If a terminal performs the back-off as describedabove, a delay may be generated in a control plane. However, consecutivecollision of random access can be avoid.

Hereinafter, a procedure for transmitting downlink data generationindication information from a base station to a terminal if there ispacket data to transmit the terminal will be described.

In a conventional cellular system, terminals in an idle state perform alow power consuming operation using discontinuous reception cycle (DRX).The terminals in the idle state include no radio bearer that is aconnection path for transmitting and receiving data on wireless channel.A procedure for informing the terminals in the idle state about downlinkdata generation by a base station is performed through a pagingprocedure. Such a paging procedure is performed by radio resourcecontrol in a base station.

However, in a packet-based mobile communication system, terminals, set aradio bearer to a base station according to the burst characteristic ofpacket data, performs a low power consuming operation using adiscontinuous reception cycle (DRX) and a discontinuous transmissioncycle (DTX), which are set by a base station. Therefore, a procedure forinforming terminals performing a low power consuming operation about thedownlink packet generation is divided into a paging procedure,hereinafter RRC paging, for terminals performing a low power consumingoperation in an idle state RRC_IDLE where a radio bearer is not set, anda downlink data generation informing procedure, hereinafter MAC paging,for terminals performing a low power consuming operation in a RRCconnected state RRC_CONNECTED where a radio bearer is set.

The RRC paging may be triggered by RRC using an additional pagingindication channel (PICH) of a physical channel. Also, MAC paging caninform terminals about the necessity of receiving a MAC paging messageby setting an indicator of a physical channel.

The MAC paging is triggered by a MAC layer, and different DRX/DTX cyclesmay be applied according to a service provided to a terminal. Also,since both of a RRC paging message and a MAC paging message have similarproperty which are transmitted for terminals performing a low powerconsuming operation, they may be managed together.

FIG. 2 is a diagram illustrating the transmission of data generationindication information for informing the generation of downlink packetdata using radio resources allocated based on uplink schedulinginformation using a group scheduling identifier in accordance with anembodiment of the present invention.

If downlink data generation indication information is transmitted usingradio resources allocated based on downlink scheduling information,radio resources are suitably allocated according to whether informationfor informing downlink data generation is present or not and accordingto the size of the information. Also, the most robust adaptivemodulation and coding scheme may be used to transmit the downlink datageneration indication information if it is necessary.

As shown in FIG. 2, a part of radio resource allocation information 13in downlink scheduling information 12 is set to transmit downlink datageneration indication information. The radio resource allocationinformation includes information about a scheduling identifier, anallocated radio resource location, and a radio resource allocationduration. Herein, the scheduling identifier is a scheduling identifieruniquely allocated to each of the terminals or a group schedulingidentifier that is reserved and allocated for downlink data generationindication information. The allocated radio resource block locationinformation denotes a location of downlink data generation indicationinformation allocated to a shared radio resource. The downlink datageneration indication information may be variably local-allocated 25-1or distributed-allocated 25-2 according to the amount of informationtransmitted to a terminal.

In case of RRC paging, RRC forms a paging channel (PCH) at a transportchannel using paging information if the paging information is generatedfor a terminal or a group of terminals at a given time. A scheduler in aMAC schedules broadcasting channel information formed in a radio frameunit, the generated paging channel (PCH) information, and trafficinformation transmitted to a terminal at every TTI.

A base station sets a PICH corresponding to a terminal or a terminalgroup in consideration of a DRX cycle for the low power consumingoperation of terminals in a RRC idle state. If a physical channel forpaging (PICH) is not set, operations related to PICH are discarded. Itmay be replaced to whether a group scheduling identifier is present ornot, which indicates scheduling information for a paging message. Then,a base station maps PCH to a radio resource block location of a physicallayer allocated in a fixed location and size in a corresponding TTIaccording to a predetermined value, modulates and codes the radioresources according to a predetermined modulation and coding scheme, andtransmits it to a terminal.

If a terminal performing a low power consuming operation according to aDRX cycle detects a PICH in a monitoring duration, the terminal preparesto receive a paging message. Accordingly, if a corresponding terminalchecks a group scheduling identifier reserved and allocated for a RRCpaging message by searching the radio resource allocation information 13in the downlink scheduling information 12, the corresponding terminalcan confirm a radio resource block where downlink data generationindication information 20 is transmitted. In this case, terminals checka RRC paging message 21 in the downlink data generation indicationinformation.

Since a base station does not store information about a correspondingterminal such as RRC context, the RRC paging message is a message forterminals that are not allocated with an unique terminal identifier suchas a scheduling identifier. Therefore, a RRC paging message may includesa terminal identifier 22 such as an international mobile subscriberidentity (IMSI) and a temporary mobile subscriber identity (TMSI), amessage part 23, and an extension bit (EB) if it necessary.

However, terminals performing a lower power consuming operation with aradio bearer include a scheduling identifier that is allocated to eachof the terminal by connecting a base station and a group schedulingidentifier that is allocated by a base station according to a group forperforming a low power consuming operation in a DRX/DTX cycle.Therefore, a scheduler of a base station can variably transmit downlinkdata generation indication information according to the number ofterminals to transmit the downlink data generation indicationinformation in a monitoring duration of a terminal performing a lowpower consuming operation at the DRX/DTX cycles and according to theamount of available radio resources at this moment.

A base station allocates radio resources for transmitting the downlinkdata generation indication information using a group schedulingidentifier when the number of terminals to transmit the downlink datageneration indication information in a monitoring duration is large andwhen the available radio resources are insufficient. In this case,terminals confirm the downlink data generation indication information 26using the radio resource block location information in the radioresource allocation information 13 if the terminal detects a groupscheduling identifier allocated to an own low power consuming operationgroup. The downlink data generation indication information may be formedusing a scheduling identifier 6 allocated to each terminal, a messagefor MAC paging 24, and an extension bit 11.

Meanwhile, a base station can form radio resource allocation informationin downlink scheduling information using a scheduling identifierallocated to each of terminals instead of using a group schedulingidentifier when the number of terminals to transmit the downlink datageneration indication information in a monitoring duration is small andwhen the available radio resources are sufficient. In this case,terminals confirm downlink data generation indication information 27using radio resource block location information in radio resourceallocation information if an own scheduling identifier is detected bysearching the downlink scheduling information in a monitoring duration.In this case, the downlink data generation indication information may beformed as a message 24.

The MAC paging message 24 or the message 24 are a message to betransmitted from a base station to a terminal for MAC paging. The MACpaging message 24 or the message 24 include information for randomaccess if a terminal needs to perform random access as a response forMAC paging, for example, information about a pre-allocated preamble tobe used for random access.

Therefore, terminals performing a low power consuming operationdetermine whether oneself is paged or not by determining whether an ownscheduling identifier allocated to oneself without RRC paging and MACpaging distinguished or a group scheduling identifier is included or notwhen the terminals search radio resource allocation information indownlink scheduling information in a monitoring duration.

FIG. 3 is a diagram illustrating reserving and using a group schedulingidentifier allocated for transmitting a part of a scheduling identifier,grant information, and downlink data generation indication informationfor scheduling radio resources in accordance with an embodiment of thepresent invention.

If a scheduling identifier is reserved and used, a scheduler allocatesscheduling identifiers to each of terminals except a group schedulingidentifier when the terminals access a base station. A group schedulingidentifier for transmitting the grant information can be used byreserving and allocating a group scheduling identifier according to arandom access burst that is configured by a base station where therandom access burst may be a random access resource region expressed ina frequency and a time. Also, a group scheduling identifier fortransmitting downlink data generation indication information can be usedby reserving and allocating an additional group scheduling identifier toeach group for low power consuming operations based on a predeterminedcriteria. Such a group scheduling identifier can be broadcasted in abase station using a broadcast channel (BCH) as system information. Onthe contrary, a base station can transmit a group scheduling identifierof a corresponding group to terminals when the base station transmitsinformation such as DRX cycle to terminal.

In FIG. 3, a reference numeral 18 denotes a group scheduling identifierreserved and allocated for transmitting response information for randomaccess, and a reference numeral 19 denotes a group scheduling identifierallocated for transmitting paging message or downlink data generationindication information. As described above, the group schedulingidentifier may be broadcasted through a broadcast channel (BCH) withsystem information or separately transmitted to each of terminals.

FIG. 4 is a diagram illustrating exclusively allocating and usingdistributed and allocated radio resources for transmitting downlinkcontrol information.

As shown in FIG. 4, downlink radio resources can be reserved, allocatedand used for transmitting response information for random access andinformation for informing downlink data generation. A base stationreserves and allocates downlink distributed allocated radio resourceblock or channel for transmitting control information transmitted to adownlink such as the response information for random access and theinformation for informing downlink data generation at an assignedlocation of TTI and broadcasts the allocated information with systeminformation to entire base station through a broadcasting channel (BCH).Since terminals detect a block or a channel among downlink radioresources, which is used to transmit the response information for randomaccess and the information for informing downlink data generationthrough a broadcasting channel, the terminals do not need additionalcontrol information for addressing a downlink radio resource block orchannel to transmit the control information of a downlink. If uplinkcontrol information to transmit to a downlink is not present in a TTI, aradio resource block or channel which is assigned and reserved totransmit control information using downlink scheduling information canbe variably used for transmitting another information.

In FIG. 4, a reference numeral 31 denotes a radio resource distributedand allocated for transmitting grant information, a reference numeral 32denotes a radio resource distributed and allocated for transmittingdownlink data generation indication information, and a reference numeral33 denotes a radio resource distributed and allocated for transmittingresponse information for sustaining uplink synchronization of a physicallayer.

While the present invention has been described with respect to certainpreferred embodiments, it will be apparent to those skilled in the artthat various changes and modifications may be made without departingfrom the spirits and scope of the invention as defined in the followingclaims.

As described above, the method for transmitting and receiving downlinkcontrol information in a packet-based cellular system according to anembodiment present invention can maximize the use of limited radioresource by effectively forming a uplink signaling message to transmitfrom a base station to a terminal and transmitting the formed uplinksignaling message with minimum radio resource occupied.

What is claimed is:
 1. A method for performing random access in aterminal of a wireless communication system, the method comprising:receiving, when downlink data is generated in a Radio Resource ControlConnection (RRC_CONNECTED) state, an information indicating a randomaccess preamble used for the random access from a base station; andtransmitting the random access preamble corresponding to the informationto the base station.